Silver halide photographic light-sensitive materials are often stored for a long period from preparation to use. The storage period sometimes exceeds 1 year. Therefore, the qualities of the photographic light-sensitive materials are required to be stable, even after stored for a long period. Under the requirement, various stabilizers have been proposed for the photographic light-sensitive materials. The stabilizers are described in detail in E. J. Birr, "STABILIZATION OF PHOTOGRAPHIC SILVER HALIDE EMULSIONS" (Focal Press).
Typical stabilizers are nitrogen-containing heterocyclic compounds. The nitrogen-containing heterocyclic compounds have an effect of preventing fog to stabilize photographic properties while the photographic light-sensitive material is prepared, stored or processed. Details of the nitrogen-containing heterocyclic compounds are described in Research Disclosure, vol. 307, pp. 866 and 869 (1989).
Most of the nitrogen-containing heterocyclic compounds function as the stabilizers when they are adsorbed on silver halide grains. Accordingly, an adsorption promoting group such as mercapto is often introduced into the nitrogen-containing heterocyclic compounds. A nitrogen-containing mercapto heterocyclic compound, however, sometimes reduces a sensitivity of the silver halide emulsion layer.
The problem of the nitrogen-containing mercapto heterocyclic compound has been solved by inventions described in British Patents No. 1079061 and No. 1289424. In the photographic material described in each of those publications, a nitrogen-containing mercapto heterocyclic compound is used in combination with a salt of silver, mercury, cadmium, copper, lead, nickel or cobalt. The metal salt has a function of preventing reduction of sensitivity caused by the nitrogen-containing mercapto heterocyclic compound.
By the way, spectral sensitizing dyes function when they are adsorbed on the silver halide grains. The stabilizers are competitive with the sensitizing dyes with respect to adsorption on the silver halide grains. Accordingly, the stabilizers make the dyes desorbed from the silver halide grains. As a result, the spectral sensitivity of the emulsion is reduced. The influence of a stabilizer is very serious when the silver halide grains have a low content of silver iodide, since the sensitizing dyes are particularly adsorbed on silver iodide rather than silver chloride or silver bromide.